This project is concerned with defining the cellular response in the hypophysis (partes distalis and tuberalis) to estrogen and progestins, including oral contraceptive agents. This involves first a satisfactory differentiation of the cellular origins of FSH, LH and TSH at both the light and electron microscopic levels of observation. This problem is being attacked with immunocytochemistry. In analyzing the feedback action of steroids, both direct and indirect pathways are being examined. The latter involves observation of the hypothalamus. Rats, monkeys and man are the subjects for study.